Can we have some first sources, please?
blogs.law.harvard.edu
blogs.law.harvard.edu
Certainly, if you discuss or analyse an article or document which is available online, link to it for the benefit of your audience (and the original author). (Exceptions like discussing a hate crimes page and not wanting to give it google-juice are fine, just let us know you're doing it.)
But the OP seems to blur this with other sources not already available on the web (or, presumably for example, behind a paywall). Are you asking for these to be uploaded, which is potentially copyright infringement and at least may go against the original author's intent?
If I review a book, do you need the primary source included?
My pet peeve is articles which are obviously inspired by journal articles but which don't even link to abstracts. Just about every journal article has a free abstract online.
The important thing is to establish a chain of reference. Obviously, linking to a full-text original source is even better, but the chain of reference is incredibly valuable.
In fact Amazon use the ISBN as part of the url for books.